Question

我正在学习带有注释和自动接线的Springs。我尝试了三种类型的自动接线

构造函数
固定注射
方法

这是我的配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd
                           http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context.xsd">

    <!-- add entry for component scanning -->
    <context:component-scan base-package="com.aht.spring.entity"></context:component-scan>

</beans>

这些是我的实体

Coach.java

package com.aht.spring.entity.coach;

public interface Coach {

    String getDailyWorkOut();

    String getDailyFortune();
}

FortuneService

package com.aht.spring.entity.fortune;

public interface FortuneService {

    String getFortune();
}

HappyFortuneService

package com.aht.spring.entity.fortune;

import org.springframework.stereotype.Component;

@Component
public class HappyFortuneService implements FortuneService {

    public String getFortune() {
        return "Feel energetic for first half of trainning";
    }
}

足球教练

package com.aht.spring.entity.coach;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.aht.spring.entity.fortune.FortuneService;

@Component
public class FootBallCoach implements Coach {

    private FortuneService fortuneService;

    @Autowired
    public FootBallCoach(FortuneService fortuneService) {
        this.fortuneService = fortuneService;
    }

    public String getDailyWorkOut() {
        return "Practice one-on-one for 2 hours";
    }

    public String getDailyFortune() {
        return fortuneService.getFortune();
    }
}

板球教练

package com.aht.spring.entity.coach;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.aht.spring.entity.fortune.FortuneService;

@Component
public class CricketCoach implements Coach {

    private FortuneService fortuneService;

    public CricketCoach() {
        System.out.println("Default constructor");
    }

    @Autowired
    public void setFortuneService(FortuneService fortuneService) {
        this.fortuneService = fortuneService;
    }

    public String getDailyWorkOut() {
        return "Practice out field tips";
    }

    public String getDailyFortune() {
        return fortuneService.getFortune();
    }
}

BaseBallCoach

package com.aht.spring.entity.coach;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.aht.spring.entity.fortune.FortuneService;

@Component
public class BaseBallCoach implements Coach {

    private FortuneService fortuneService;

    public String getDailyWorkOut() {
        return "Practice curve whole day";
    }

    public String getDailyFortune() {
        return fortuneService.getFortune();
    }

    @Autowired
    public void customAutoWire(FortuneService fortuneService) {
        this.fortuneService = fortuneService;
    }
}

我有三个用于执行三种自动接线方式的类，构造函数和设置器工作正常，但是当完成method明智的自动接线时，就会调用错误的构造函数。我在BaseBallCoach类中错过的一件事是默认构造函数，但是无论如何，编译器会自动为我生成一个吗？

这是我的 CoachMethodInjectionApp.java ，我在其中执行方法自动接线

package com.aht.spring.app;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.aht.spring.entity.coach.Coach;

public class CoachMethodInjectionApp {

    public static void main(String[] args) {

        //  read config-file
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

        //  get beans
        Coach coach = context.getBean("baseBallCoach", Coach.class);

        //  get dependencies
        System.out.println(coach.getDailyFortune());

        //  get daily workout
        System.out.println(coach.getDailyWorkOut());

        //  close context
        context.close();
    }
}

这是输出

Default constructor
Feel energetic for first half of trainning
Practice curve whole day

输出的第一行是我不了解的Default constructor，为什么要执行CricketCoach的构造函数？

Answer 1

由于CricketCoach类带有@Component注释，并且在Spring容器启动时扫描包，它将通过调用no-arg构造函数来创建类型为CricketCoach的实例

所有在xml文件中定义或用@Component注释或从扫描到的软件包进行@Component的扩展名的bean都将在spring容器启动时创建，无论是否使用它们

Answer 2

您要在此处创建Coach类的新实例： Coach coach = context.getBean("baseBallCoach", Coach.class); 每次创建新实例时，它都会执行一个构造函数。您已在其中致电System.out.println("Default constructor");。您可以尝试从板球教练训练中删除@Component。

Spring Autowiring调用错误的构造函数

2 个答案: